Amplifier connection



Get. 23, 1928.

1,688,701 F. GEHRTS AMPLIFIER CONNECTION Filed Sept. 10, 1925 Inventor: Friedrich Gehr'ts,

bywpgif His Attorney.

Patented Oct. 23, 1928.

' UNITED STATES PATENT OFFICE.

FRIEDRICH GEHRTS, OF KARLSI-IORST, NEAR BERLIN, GERMANY, ASSIGNOR TO GEN- ERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

AMPLIFIER CONNECTION.

Application filed September 10, 1923, Serial No. 661,739, and in Germany November 7, 1922.

In the connectionof line conductors in duplex telephone connections with intermediate amplifiers the impedance of the two lines connected by the intermediate ampli- 5 fiers or the impedance of each one of the lines and the artificial reproduction of the same must be carefully equalized in their dependency on the frequency. If this is not the case, back coupling takes place, so that a disturbing whistling of the'amplifier is heard, whenever a certain degree of amplification Y is exceeded.

It is not possible in practice to obtain the equalization between the impedance of a line conductor and its artificial reproduction for all frequencies. As shown by theory and practice, the difficulties of the reproduction are especially great in the neighborhood of the natural frequency of the line conductor even with a careful reproduction of the impedance, as given by the method of calcu lation by R. S. Hoyt in the U. S. Patent No. 1,167,693 and by K. Kopfmiiller in German Patent 330,964. The maintenance of equality between the line conductor and its reproduction is poor and the danger of whistling accordingly great. My present invention consists in reducing the difliculties of equalization to a minimum,

'30 in that in the elements of the amplifier connection are inserted connecting means, for example, condensers, self-inductances and resistances, which are automatically variable according to the direction of speaking, so that the development of a disturbing autoexcitation, especially also within the range of the frequencies in the neighborhood of the natural frequency of the line conductor, is

avoided. The means for obtaining such an 40 action can be, for example, a choke coil, the inductance of which can generally be kept small by pre-magnetization, which latter is then. compensated by a counter-magnetization, which becomes effective at the moment talking is started in the other direction. The counter nagnetization can also be obtained by means of a direction amplifier or similar rectifying arrangements.

The mode of operation of the connection is as follows By means of the auxiliary magnetization the ch eke coil is premagnetized to beyond its saturation point and its impedance is relatively small. sit the moment, however, when the premagnetization is compensated by the c;)untermagnetizing current, the inductance of the coils increases and therewith their impedance in accordance wtih the frequency range to be choked. The back coupling of the amplifier and Whistling or the generation of oscillations are correspondingly reduced in the critical frequency range when the impedance is increased.

An example of one way of carrying out my invention is shown in the drawing, I have indicated a duplex connection in which there is arranged for each line an artificial line K1 and K1,. For each talking direction there is provided an amplifying tube R and R and there is also in each line a direction amplifier B 1 and R 1, which rectify a part of the talking currents after having been amplified. In order to obtain a. favorable current curve for he compensation magnetization current two direction amplifiers can be employed instead of one.

The choke coil D7, which lies in conductor F R F is premagnetized by the winding S The talking currents arriving over the incoming line F pass through the device R windings W and X of the coil D1" and thence to the line F They also pass through the device R,1 and are then conducted after being amplified to the winding T, of the choke coil Dig, in such manner that there is produced in this winding a c0unter-magnetization compensating the premagnetization. At the same time the amplifierR transmits the am plified talking currents over' the windings W and X of the choke coil to the outgoing line These talking currents now produce at the same time, in conjunction with the magnetization compensating current a change in the choking limits of the coil for the critical frequency range. Disturbing frequencies can furthermore be eliminated in the known manner by parallel connected capacities C and by choke coils D connected up to the anode circuit of the direction am- The direction amplifier R 1 and the choke coil Dr, operate in the same manner for the current coming from the line F Talking currents which arrive over the line F pass through the amplifier R windings W and X of the coil D1", and thence to the line F They also pass to the device R 1 where they are caused to produce a magnetization of the winding T, which is counter to the premagnetlzation resulting from energization of) the winding S What I claim as new and desire to secure by Letters Patent of the United States is:-- i

'for automatically increasing the value of said impedance,

2. The combination in a duplex telephone amplifier system of an inductance comprising a winding connected in each current path and means independent of said winding responsive to talking currents transmitted over thepath in which said inductance is connected for automatically increasing the value of said inductance.

3. The combination in a duplex telephone amplifier system of an i edance in each current path and means inc uding a thermionic device for automatically varying the value of each impedance in accordance with the talking direction and thereby preventing the generation of oscillations.

4. The combination in a duplex telephone amplifier system of an inductance in each current path and means including a thermionic device for automatically varying the value of each inductance in accordance with the talking direction and thereby preventing the generation of oscillations.

5. The combination in a duplex telephone amplifier system of an iron core and a winding connected in each current path, means for producing a steady magnetization of each core, and means including an additional winding controlled by talking currents for producing a variable magnetization of each core in the opposite direction to the constant magnetization.

6. The combination in a duplex telephone amplifier system of an iron core and a winding connected in each current path, means for producing a steady magnetization of each core. and means including an additional winding for automatically decreasing the magnetization of each core whenever talking currents are transmitted over the path in which the first mentioned winding is connected.

7. The combination in a duplex telephone amplifier system of an iron core and a windtransmitted over the path in which the first mentioned winding is connected.

8. .The combination in a duplex telephone amplifier system of an incoming line and an outgoing line, means for amplifying a'portion of the currents received over the incoming line and delivering am lified currents to the outgoing line, an impe ance connected to the outgoing line and means controlled by another portion of the currents received over the incoming line for varying the value of the impedance in the outgoing line.

9. The combination in a duplex telephone amplifier system of an incoming line and an outgoing line, means for amplifying a portion of the currents received over the incoming line and delivering amplified currents to the outgoing line, an inductance connected to the outgoing line and means controlled by another portion of the currents received over the incoming line for varying the value of the inductance in the outgoing line.

10. The combination in a duplex telephone amplifier system of an incoming line and an outgoing line, means for amplifying a portion of the currents received over the incomingline and delivering amplified currents to the outgoing line, an iron core inductance connected in the outgoing line, means for producing a steady magnetization of the core of said inductance, and means controlled by' another vportion of the received currents for varying the magnetization of said core.

11. The combination of a duplex telephone amplifier system of an incoming line and an outgoing line, means foramplifying one portion of the currents received over the mcoming line and delivering amplified currents to the outgoing line, an iron core inductance connected in the outgoin line having a magnetizing winding to whic 1 a steady current is supplied and a magnetizing winding to which another portion of the received currents are supplied, and means for amplifying and rectifying said latter portion of the received currents.

In witness whereof, I have hereunto set my hand this 17th day of August, 1923.

FRIEDRICH GEHR-TS.

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